Although nitrous oxide has been widely used since 1844, it has in recent years been implicated in a number of serious health hazards such as reproductive, nerve, liver and kidney disorders. Animal studies have implicated chronic low level exposure to nitrous oxide with fertility problems in both male and female rats. Human data indicate a 100% increase in involuntary infertility among female anaesthetists. Preliminary work in our laboratories indicated that acute exposure disrupts ovulation in female rats. Critical to fertility and, therefore, reproduction is the process of ovulation. Luteinizing hormone releasing hormone (LHRH) plays a central role in this process, with its neurosecretion of LH from the pituitary. This brings about a series of events initiating ovulation and leading to fertilization. However, LHRH secretion itself is controlled by a number of hormonal and neural factors. Beta-endorphin appears to be involved in the neural regulation of LHRH secretion and may be affected by nitrous oxide exposure. In this study both acute high and chronic low levels of nitrous oxide will be used. Changes in the ovulatory cycle will be assessed by vaginal smears. Brains from both exposed and control animals will be removed and immunopositive LHRH Beta-endorphin neurons and terminals will be immunocytochemically localized. Comparisons will be made between exposed and non-exposed female rats, exposed on different days of the ovulatory cycle and acute versus chronic exposure. Data will be analyzed using computerized image analysis and three-dimensional reconstruction of the LHRH and Beta-endorphin systems. Brain levels of LHRH and Beta-endorphin will be determined by RIA. Blood samples will be taken from animals being used for immunocytochemistry as well as those being used for RIA. This will allow for direct measurement of serum LH.